I've done some more research and have come to the conclusion that
Quartz QCRenderer must be performing color correction (or distortion,
depending on your pt of view) under 10.4. (I'd love to be wrong
about this - really).
I'm wondering if anyone has anything they can add to this, or even
better a "oh yeah, do XYZ and you might find it'll work". I've
created a reasonably small test harness that demonstrates the
problem. It simply grabs the screen and puts it into a SampleCIView.
Here's what I've discovered:
1) The most basic test. Clip a 128x128 area around the mouse (out of
the CVPixelBufferRef that contains the image from the screen).
Composite this back onto the final image before it's passed to the
SampleCIView, but at an offset y + 2 (so that we can see that the
compositing is taking place). Indeed, we can see a bit of the image
being composited on and the colors are correct.
Note: The primary reason for testing this was to check that my own
compositing code wasn't introducing the color change.
2) Do the same as (1) above, but before compositing pass the 128x128
buffer into a "do nothing" quartz patch. This patch takes a CIImage
as input, transforms it (upside down) using an Affine Transform and
spits it out again. It's got a (1) Clear and (2) Billboard of size
2.0. I'd not expect this to have any real effect on the image. What
I see however is a lightening of the 128x128 image when it is
composited.
Is it the case that all ye who enter the realm that is QCRenderer on
10.4 should abandon all hope (of getting color correct)?
BTW: This code works fine under 10.5.
I've posted a full example, with controls to disable the QC part (so,
perform step (1) above) and also the offset. So that whoever wants to
can see the issues easily. I'm happy to raise a radar for this if
it's appropriate, but I'd like to know if I'm doing something silly/
stupid first.
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